Open a JS file and edit a line with Python

Question

I'm trying to modify a specific line in a js file using python.

Here's the js file :

...
hide: [""]
...

Here's my python code :

with open('./config.js','r') as f:
   lines = f.readlines()

with open('./config.js','w') as f:
   for line in lines:
       line = line.replace('hide', 'something')
       f.write(line)

So it works but this is not what I want to do.

I want to write 'something' between the brackets and not replace 'hide'.

So I don't know how to do it: Do I have to replace the whole line or can I just add a word between the brackets?

Thanks

Would you try `line = line.replace('hide', 'hide: [\"something\"]')`? — Geno Chen, Nov 23 '18 at 08:57

Filip Młynarski · Accepted Answer · 2018-11-23T10:15:10.740

4

If you want to replace text at this exact line you could just do:

with open('./config.js','r') as f:
   lines = f.readlines()

with open('./config.js','w') as f:
   new_value = 'Something New'
   for line in lines:
       if line.startswith('hide'):
           line = 'hide: ["{}"]'.format(new_value)
       f.write(line)

or alternatively in the conditional

           if line.startswith('hide'):
               line = line.replace('""', '"Something new"')

Here's way to replace any value in brackets for hide that starts with any spacing.

lines = '''\
first line
            hide: [""]
       hide: ["something"]
last line\
'''
new_value = 'new value'

for line in lines.splitlines():
    if line.strip().startswith('hide'):
       line = line[:line.index('[')+2] + new_value + line[line.index(']')-1:]
    print(line)

Output:

first line
            hide: ["new value"]
       hide: ["new value"]
last line

edited Nov 23 '18 at 10:15

answered Nov 23 '18 at 08:57

Filip Młynarski

3,534
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10
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what if `hide: [""]` not alone in line? – Andrey Topoleov Nov 23 '18 at 09:03
I think that's what author meant and why I said it will replace only this exact line – Filip Młynarski Nov 23 '18 at 09:05
hide is alone in line – William Nov 23 '18 at 09:20
There is a way to change whatever there is between the brackets ? For exapme if I have "something" and the next time "somethingelse" without modifying my python code – William Nov 23 '18 at 09:27
Updated my answer based on @SpghttCd idea. – Filip Młynarski Nov 23 '18 at 09:40
Glad to have been of help! – Filip Młynarski Nov 23 '18 at 09:55
Ah ! And last question : I have like 15 spaces before 'hide' so when i put it in my code this is ugly. There is a way that python takes them into consideration without copy/paste 15 spaces ? if it's too complicated don't worry I'll go with that which is already super fine – William Nov 23 '18 at 09:57
Updated my answer, you can try it. – Filip Młynarski Nov 23 '18 at 10:15
Perfect, you're the boss :p – William Nov 23 '18 at 10:27
Just for the sake of ease and readability: for this issue imo the `replace`-approach would fit better than searching for bracket's indices. But anyway, now you should have anything you need, so you can pick what you like... :) – SpghttCd Nov 23 '18 at 11:09
`replace` shown in your example will work only if value of hide is `[""]`, using brackets searching replace whatever's between them. – Filip Młynarski Nov 23 '18 at 11:25

SpghttCd · Answer 2 · 2018-11-23T09:19:33.027

1

If hide: [""] is not ambiguous, you could simply load the whole file, replace and write it back:

newline = 'Something new'

with open('./config.js','r') as f:
   txt = f.read()

txt = txt.replace('hide: [""]', 'hide: ["' + newline + '"]')

with open('./config.js','w') as f:
   f.write(txt)

edited Nov 23 '18 at 09:19

answered Nov 23 '18 at 09:12

SpghttCd

10,510
2
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score 1 · Answer 3 · answered Nov 23 '18 at 09:15

You can use fileinput and replace it inplace:

import fileinput
import sys

def replaceAll(file,searchExp,replaceExp):
    for line in fileinput.input(file, inplace=1):
        if searchExp in line:
            line = line.replace(searchExp,replaceExp)
        sys.stdout.write(line)

replaceAll("config.js",'hide: [""]','hide: ["something"]')

Reference

slackline · Answer 4 · 2018-11-23T09:08:46.557

You can do this using re.sub()

import re
with open('./config.js','r') as f:
   lines = f.readlines()

with open('./config.js','w') as f:
   for line in lines:
       line = re.sub(r'(\[")("\])', r'\1' + 'something' + r'\2', line)
       f.write(line)

It works by searching for a regular expression, but forms a group out of what you want on the left ((\[")) and the right (("\])). You then concatenate these either side of the text you want to insert (in this example 'something').

The bounding ( ) makes a group which can be accessed in the replace with r'\1', then second group is r'\2'.

score 0 · Answer 5 · answered Nov 23 '18 at 09:04

As long as you don't have "hide" anywhere else in the file, then you could just do

with open('/config.js','r') as f:
    lines = f.readlines()

with open('./config.js','w') as f:
    for line in lines:
        line = line.replace('hide [""]', 'hide ["something"]')
        f.write(line)

Open a JS file and edit a line with Python

5 Answers5